In current biodiesel production processes, crude glycerol is produced as a major by-product in an amount corresponding to about 10% (w/w) of the total amount of products (Johnson and Taconi, Environ Prog, 26:338, 2007). Such crude glycerol has an impact on the market price of glycerol and is also considered a cause of environmental problems because it is not permitted to discharge such crude glycerol directly to the environment (da Silva et al. Biotechnol Adv, 27:30, 2009). For these reasons, methods have been developed in order to convert inexpensive crude glycerol to fuels and industrially valuable substances, including physiologically active substances.
Glycerol can be converted to a variety of chemical raw materials by microbial fermentation, and a typical example of such chemical raw materials is 1,3-propanediol. 1,3-propanediol can be used as a raw material for synthesizing polyester, polyether or polyurethanes, and is used in various applications, including textiles such as highly functional clothes, carpets or vehicle textiles, and plastic films. In particular, polytrimethylene terephtalate (PTT) that is produced by polymerization of 1,3-propanediol and terephthalic acid has excellent physical properties and a melting point of 228° C., which is lower than that of polyethylene terephtalate (PET), and thus the actual usefulness thereof is higher. Accordingly, PTT is attracting attention as a next-generation fiber material. Furthermore, plastic and polymer products made using 1,3-propanediol as a monomer shows better optical stability than products made using butanediol or ethylene glycol. In addition, 1,3-propanediol can be used as a polyglycol-type lubricant and a solvent, and thus is evaluated to have a higher commercial value than glycerol.
Up to date, a glycerol-fermenting microorganism reported to show the highest production of 1,3-propanediol is Klebsiella pneumoniae, and studies on the glycerol fermentation metabolic pathways of Klebsiella pneumoniae have been actively conducted (FIG. 1). Klebsiella pneumoniae produces 1,3-propanediol by reduction of glycerol and, at the same time, produces large amounts of competitive metabolites such as 2,3-butanediol by oxidation of glycerol. Thus, attempts have been actively made to promote the production of 1,3-propanediol by inhibiting the production of major competitive metabolites in Klebsiella pneumoniae. It was typically found that the production of 1,3-propanediol can be increased by inhibiting the production of lactic acid in a mutant wherein lactate dehydrogenase is deleted (Oh et al. Appl Biochem Biotechnol 166:127-137, 2012). Inhibition of the production of competitive metabolites in Klebsiella pneumoniae is very advantageous not only for promotion of the production of 1,3-propanediol, but also for efficient purification of 1,3-propanediol. In particular, because 2,3-butanediol that is a major competitive metabolite has physicochemical properties very similar to those of 1,3-propanediol, it acts as a big obstacle in purification of 1,3-propanediol when it is present in a mixture with 1,3-propanediol. In recent years, several research groups have developed mutants wherein a 2,3-butandiol synthetic pathway is deleted in Klebsiella pneumonia (Oh et al. Appl Biochem Biotechnol 166:127-137, 2012). However, it was shown that the production of 1,3-propanediol in the mutant lacking the 2,3-butandiol synthetic pathway decreased while the fermentative metabolism of glycerol and the growth of cells were reduced, although the reason therefor has not yet been clear.
Accordingly, the present inventors have made extensive efforts to develop a method of increasing the production of 1,3-propanediol in a mutant lacking the 2,3-butanediol synthetic pathway, and as a result, have found that, when a mutant strain expressing the pyruvate decarboxylase and aldehyde dehydrogenase genes is used, the production yield of 1,3-propanediol can be increased while the production of 2,3-butanediol is inhibited, thereby completing the present invention.